The present specification basically relates to energy/power saving in communication networks.
Low power consumption is to be considered an important performance indicator for communication networks and the users of a cellular phone. Today, the power consumption of a user equipment (UE) is typically described in terms of battery life time and, more specifically, talk time and standby time. On the network side, the power consumption is mainly described by the power consumption of access nodes (such as base stations), and is typically measured for different configuration and load assumptions. In principle the access node power consumption for zero load over the air interface could be seen then as standby time power leakage of the access system. In future, it is expected that energy related measures are playing a more and more important role in the design and configuration of a competitive future radio access network.
Therefore, and to support energy efficient radio access networks, 3GPP (Third Generation Partnership Project) has introduced higher layer procedures for base station (access node) switch-off or switch-on (wake-up). The procedures in general can be distinguished to be controlled autonomously at the base station (access node) or centrally e.g. via an OAM (Operation Administration and Maintenance) entity.
While energy/power saving is generally applicable in all kinds of communication networks, certain efforts in this regard have already been made specifically in the context of heterogeneous network environments. Accordingly, such heterogeneous network environments are taken as a non-limiting example in the remainder of the present specification.
In the development of cellular systems in general, and access networks in particular, heterogeneous network environments, also referred to as multi-layer cellular network systems, comprising a combination of macro or overlay cells and micro or underlay cells (also referred to as pico cells or femto cells) are proposed as one concept. Thereby, the macro cells (having high transmit power) typically provide for a large geographical coverage, while the micro cells (having low transmit power) typically provide for additional capacity of low geographical coverage in areas with a high user deployment. Thus, the macro cell layer is also referred to as coverage layer, and the micro cell layer is also referred to as capacity layer or capacity boosting layer. In the context of LTE or LTE-Advanced (LTE: Long Term Evolution), the macro cells are typically deployed by access nodes or base stations denoted as eNBs, while micro cells are typically deployed by access nodes or capacity transmission nodes such as home base stations denoted as HeNBs, pico base stations, relay nodes, or the like. Such heterogeneous network environment may, thus, be considered to be composed at least of two network layers, i.e. an underlay (micro cell) layer and an overlay (macro cell) layer.
A specific example of a heterogeneous network environment is a relay-enhanced cellular system. In relaying, a terminal or user equipment (UE) is not directly connected with an access node such as a radio base station (e.g. denoted as eNodeB or eNB) of a radio access network (RAN), but via a relay node (RN) which is connected to the access node. In this case, the underlay (micro cell) layer is constituted by relay (access) nodes.
The two network layers of a heterogeneous network environment, i.e. the access nodes (base stations) and/or cells of the two network layers, may be implemented by the same radio access technologies. For example, a heterogeneous network environment may be composed of an LTE-based macro cell layer and an LTE-based micro cell layer. Herein, such deployment is typically referred to as inter-eNB scenario.
The two network layers of a heterogeneous network environment, i.e. the access nodes (base stations) and/or cells of the two network layers, may also be implemented by different radio access technologies. For example, a heterogeneous network environment may be composed of a 2G/3G-based macro cell layer (2G/3G: Second/Third Generation of Mobile Communications) and a LTE-based micro cell layer. Herein, such deployment is referred to as inter-RAT (radio access technology) scenario.
Multi-layer or heterogeneous (e.g. LTE-based) networks might be deployed using co-channel deployment, dedicate carrier deployment, or a combination of those. In co-channel deployment, both the macro and micro access nodes (base stations) are using the same carrier frequency. In dedicate carrier deployment, macro and micro access nodes (base stations) are using different carrier frequencies.
In the context of heterogeneous network environments, to reduce the network power consumption in heterogeneous networks without harming the system performance in both aforementioned deployment scenarios, the above-mentioned energy/power saving procedures are specifically directed to switch off the capacity transmission/boosting nodes/cells of the micro layer, such as home base stations, pico base stations, relay nodes, or the like, and to serve the respective users by the coverage nodes/cells of the macro layer, such as base stations. This is particularly feasible during low traffic periods (e.g. at night and during off peak network times) when the macro layer alone is capable to serve all of the remaining traffic requests.
In this regard, the main problem is to determine the correct or best suited nodes/cells of the micro layer to switch on again after their switch-off, when needed. That is, when the capacity transmission/boosting nodes/cells are not active and the load increases, the serving coverage nodes/cells could not know which micro node/cell should be activated, especially when the increasing load is concentrated in one or a few hotspots of the micro layer.
Stated in other words, the main problem is to find the best candidate for activation among possible micro layer nodes/cells in order to achieve the most effective offload result.
For this problem, several approaches have already been proposed, as outlined hereinafter.
A first conceivable approach is based on pre-defined high load/low load periods for each hotspot (which are most probably derived from historical traffic statistic data). The hotspot (s) with the highest/high (historical) load is chosen to be switched on. This approach suffers from the usage of historical and static (non-dynamic) data, thus being incapable to cope with dynamical changes such as short-term fluctuations or longer-term trends.
A second conceivable approach is to switch on all hotspots at first, and to switch off again those hotspots which experience low/no load afterwards. This approach suffers from low energy efficiency, as well as large signaling overhead, and creates handover problems due to the intermediate activation of a hotspot which remains in operation only for a short time.
A third conceivable approach is to bring the inactive hotspots in a probing phase, in which downlink reference signals are transmitted, which signal (“pilot”) can be measured by idle and connected UEs and shall be reported to the macro cell's eNB in order to make an appropriate decision which micro layer nodes/cells to activate. This approach suffers from the fact that this probing phase requires to power on the full TX (transmit) chain at a number of deactivated hotspots and results in greatly lowered energy efficiency. Also, this approach might be completely inhibited in the intra-frequency case due to potential interference issues.
A fourth conceivable approach is mainly based on UE positioning methods. However, this approach suffers from the low accuracy in the order of several 100 meters even in case of the proposed usage of the enhanced cell identity parameter (E-CID). Further, other more accurate positioning methods (e.g. GPS) are either not fully available or require additional efforts in terms of software and/or hardware. Another major drawback of this approach is that the pure geographical position does not provide reliable information of the coverage situation, as in real environments a cell is generally of irregular shape.
A fifth conceivable approach is to keep (or temporarily activate) the dormant hotspots in a listening mode and to observe the interference over thermal noise (IoT), wherein the IoT per hotspot is used as an indication if (or how many) active users are nearby. In a variant of this approach, a systematic error correction to mitigate the impact of pathloss adaptation of uplink power control may be additionally introduced in order to cope with a situation in which the hotspots are at different cell locations (i.e. near/far from the relevant macro layer base station). This approach has advantages of high energy efficiency (since only the RX (receive) chain needs to be kept active for short periods) and reasonable reliability. This approach suffers from disadvantages in terms of a potential activation (wake-up) of micro layer nodes, even if there are no UEs which could be served thereby, a potentially erroneous decision of activation (wake-up) of micro layer nodes due to uplink/downlink load asymmetry, and potential additional hardware requirements.
In view of the above, while the aforementioned fifth approach is considered to be most effective for energy/power saving in communication networks, especially but exclusively in heterogeneous network environments, there is still a need to further improve an access node wake-up control.
In view thereof, there is still a need to further improve an access node wake-up control so as to keep the number of active access nodes in heterogeneous deployments low in order to achieve improved and reduced network power consumption during idle periods and off peak network hours.